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Choose the correct option. In which of the following systems will the radius of the first orbit of the electron be smallest? - Physics

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Question

Choose the correct option.

In which of the following systems will the radius of the first orbit of the electron be smallest?

Options

  • Hydrogen

  • Singly ionized helium

  • Deuteron

  • Tritium

MCQ

Solution

Singly ionized helium

Explanation:

According to Bhor's theory, the radius of an atomic number z atom's nth orbit is: `r prop "n"^2/"Z"`. 

Where n is the orbit number.

(i) For hydrogen,

∴ n = 1 and Z = 1

Therefore, `r prop "n"^2/"Z"`

⇒ r ∝ 1

(ii) For Helium,

∴ n = 1 and Z = 2

Therefore, `r prop "n"^2/"Z"`

`=> "r" prop 1/2`

(iii) For Deuteron.

∴ n = 1 and Z = 1

Therefore, `r prop "n"^2/"Z"`

`=> "r" prop 1`

(iv) For Tritium,

∴ n = 1 and Z = 1

Therefore, `r prop "n"^2/"Z"`

`=> "r" prop 1`

Hence, the smallest is Helium. The correct option is Singly ionized helium.

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Structure of Atoms and Nuclei
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Chapter 15: Structure of Atoms and Nuclei - Exercises [Page 342]

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Balbharati Physics [English] 12 Standard HSC Maharashtra State Board
Chapter 15 Structure of Atoms and Nuclei
Exercises | Q 1.1 | Page 342

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